| Objective: Acinetobacter baumannii is a gram-negative non-fermentingbacteria, widely distributed in the hospital environment, including surfaces ofmedical staff, ventilator equipment, dialysis machines, and even water. A.baumannii has emerged as a leading cause of nosocomial infections, whichcan lead to a variety of hospital infections, for instance wound infection,pneumonia, septicemia and meningitis. In recent years, with the extensiveapplication of antibiotics, A. baumannii resistant strain emerged and spreadeddramatically, from single to multidrug resistance, and low to high resistance.Multidrug-resistant A. baumannii presents serious challenges for the effectivetreatment of infections diseases, so researches on the mechanism andepidemiology of Acinetobacter resistance has become a hot topic. The studyexpected to provide new data for epidemiological investigation of A.baumannii by using MLST (Multilocus sequence typing), multiplexpolymerase chain (M-PCR) reaction to study the mechanisms of drugresistance, and population structure of A. baumannii.Methods: During the period of2002-2009,341clinicalmultidrug-resistant isolates A. baumannii collected from different departments,different period patients and different specimens of a general hospital. First ofall, genomic DNA of all the strains was extracted by phenol-chloroformprotocol; secondly, potential carbapenems resistance genes were screened byM-PCR: OXA23, OXA58, OXA69, OXA143, OXA51and OXA24; finally,all341isolates were analyzed by a MLST schme including sevenhousekeeping genes to determine the ST (sequence type) of isolates. On thebasis of allelic profile and ST, we can further analyze the population structureof A. baumannii by using Bionumerics6.6, START2.0, RDP3.0, MEGA and eBURST softwares.Results:97.95%of the341isolates are positive for blaOXA-51-likegene. Ingeneral the discrepancy rate with preliminary indentification is2.05%.Meanwhile the positive rates of blaOXA-23-likeand blaISAba1were89.44%and99.41%, respectively. We failed to identify any positive strains of blaOXA-24-like,blaOXA-58-likeand blaOXA-143-like. Totally18types of resistance-associated genescombinations were revealed by the method of Multiplex PCR, and thedominating combination profile wasblaOXA-51-like+blaOXA-23-like+blaOXA69+blaISF-R+blaISF-OXA23R(n=262,76.83%) Itwas reported that ISAba1located upstream of blaOXA-23-likeor blaOXA-51-like, butin this study we found blaISAba1-OXA23and blaISAba1-OXA51existed at the sametime. The present study showed that the success rate of341strains is97.95%by MLST method.334strains were designated to4STs by Bionumerics6.6,including2novel STs. The predominating clone of multidrug resistant A.baumannii in this hospital is ST2(2-2-2-2-2-2-2), which is also the leadingepidemic clone of resistant A. baumannii worldwide. In this research, theMLST sequence types (STs)(and their percent distributions) were as follows:ST-2(97.95%), ST-113(0.9%), ST-185(0.9%), and ST-187(0.3%). ST-185,ST-187and the alleles rpoB-42, rpoB-43are described for the first time. ST2,ST185and ST187belonged to clone complex1（CC1）, and ST113belongedto clone complex8（CC8）by the analysis of eBURST software. START2.0showed ISA=0.1436(P<0.0001). It implies linkage disequilibrium andrecombination events. For a total of10recombination events were identifiedin pyrG, cpn60, fusA, gltA, rplB and recA by RDP3.0.Conclusion: The present study showed that the blaOXA-51-likegenecarrying rate was97.95%. And the major combination wasblaOXA-51-like+blaOXA-23-like+blaOXA69+blaISF-R+blaISF-OXA23R(n=262,76.83%).The spread of multidrug-resistant A. baumannii in the investigated hospitalwas closely related to ST2-CC1. A. baumannii had epidemic populationstructure. High levels of recombination happened in clonal structure, butallelic profile remained the characteristics of linkage disequilibrium. |
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